Kearney B, Staskawicz B J
Department of Plant Pathology, University of California, Berkeley 94720.
Nature. 1990 Jul 26;346(6282):385-6. doi: 10.1038/346385a0.
Disease-resistance genes introduced into cultivated plants are often rendered ineffective by the ability of pathogen populations to overcome host resistance. The bacterial pathogen Xanthomonas campestris pathovar vesicatoria causes bacterial spot disease of tomato and pepper, and this pathogen has been shown to overcome disease resistance in pepper (Capsicum annuum) by evading the recognition and defence response of the host plant. Numerous resistance genes to bacterial spot have been identified in pepper and its wild relatives, each providing resistance to specific races of X.c. vesicatoria. The resistance gene Bs1, for example, provides resistance to X.c. vesicatoria strains expressing the avirulence gene avrBs1; Bs2 provides resistance to stains expressing avrBs2 and so on. We now report that avr Bs2 is highly conserved among strains of X.c. vesicatoria, and among many other pathovars of X. campestris. Furthermore, we find that avrBs2 is in fact needed for full virulence of the pathogen on susceptible hosts. This implies that plants carrying Bs2 can recognize an essential gene of the bacterial pathogen, which may explain why Bs2 confers the only effective field resistance to X.c. vesicatoria in pepper.
导入栽培植物中的抗病基因常常会因病原菌群体克服宿主抗性的能力而失效。细菌性病原菌野油菜黄单胞菌斑点病致病变种会引发番茄和辣椒的细菌性斑点病，并且已证明这种病原菌通过逃避宿主植物的识别和防御反应来克服辣椒（辣椒属）的抗病性。在辣椒及其野生近缘种中已鉴定出许多针对细菌性斑点病的抗性基因，每个基因都对野油菜黄单胞菌斑点病致病变种的特定小种具有抗性。例如，抗性基因Bs1对表达无毒基因avrBs1的野油菜黄单胞菌斑点病致病变种菌株具有抗性；Bs2对表达avrBs2的菌株具有抗性，以此类推。我们现在报告称，avr Bs2在野油菜黄单胞菌斑点病致病变种的菌株以及野油菜黄单胞菌的许多其他致病变种中高度保守。此外，我们发现avrBs2实际上是病原菌在感病宿主上实现完全毒力所必需的。这意味着携带Bs2的植物能够识别细菌性病原菌的一个必需基因，这或许可以解释为什么Bs2赋予了辣椒对野油菜黄单胞菌斑点病致病变种唯一有效的田间抗性。
